Target for an electrostatic writing tube



Dec. 6, 1960 R. w. CREWS ET AL 2,963,606

TARGET FOR AN ELECTROSTATIC WRITING TUBE Filed May 7, 1959 & zzcrea/v flG. 19.

IN V EN TORS.

5 W a C M W 5 w P UnitedStates Patent TARGET FOR AN ELPiIC'IEROSTATIC WRITING Robert W. Crews and Philip J. Rice, Jr., Palo Alto, Calif, assignors to A. B. Dick Company Filed May 7, 1959, Ser. No. 811,757

2 Claims. (Cl. 313-73) This invention relates to electrostatic writing tubes and, more particularly, to an improved target for an electrostatic writing tube and the method of producing it.

Electrostatic writing tubes are devices usually including a cathode-ray tube which has a plurality of writing wires where a phosphor screen usually is placed. These wires extend from inside the tube to points on the outside surface of the tube face. Opposite these points is a ground plane which is maintained at anode potential. Usually a dielectric writing medium, such as paper, is passed between the ground plane and the points. The cathode-ray beam of the cathode-ray tube is directed onto a desired one of the writing wires in the face of the tubes. Thereby, the wire is charged up in potential until it exceeds a critical value, at which time a charge is deposited on the surface of the dielectric medium. The wires may be arranged in a column in the manner described and claimed in an appli cation for Electrostatic Printing System, by John L. Tregay, filed May 10, 1957, Serial No. 658,275, and assigned to a common assignee. The cathode-ray beam is continuously swept across the ends of the wires inside the tube while the dielectric writing medium continually moves past the ends of the wires outside the tube. Means are provided for maintaining the beam turned off, except when it traverses selected ones of the wires. These selected wires charge up toward the potential of the cathode of the cathode-ray tube and when a critical value with respect to the external plane is reached, a selected wire discharges. A spot of charge remains on the dielectric writing medium under the wire which is discharged. This spot of charge can be developed out to become visible. Such developing out can be done using xerographic techniques, for example.

From the above brief description, it will be appreciated that the wiring wire array consists of a number of isolated wires which have no direct-current return path to the cathode to complete the circuit, except by way of the electrical discharge which does the writing. This has a disadvantage in that there is no method of controlling the electrical discharge; that is, the discharge will continue until the wire capacitance is discharged. Because of this, a wire will sometimes continue to write longer than desired. Furthermore, before a wire can attain a discharge potential, its capacitance must also be charged up by the electron beam, thus slowing the writing process.

An object of this invention is to provide a writing Wire array for an electrostatic writing tube wherein the capacitance both inter-wire and to ground of the writing wires is reduced considerably over what it has been heretofore.

Another object of the present invention is to provide a wire-writing array for an electrostatic writing tube which achieves better resolution in writing than possible heretofore.

Yet another object of the present invention is the provision of a novel-and improved short-wire writing array for an electrostatic writing tube.

Still another object of the present invention is to provide a novel method of making an improved short wire writing array for an electrostatic writing tube.

These and other objects of the invention may be achieved by a method and means of constructing a wirewriting array as follows. First, the wire to be used for writing is wound around a rod at a desired pitch. The rod may be of any suitable dielectric material, such as glass. Next, a similar rod is sealed to the first rod by means of an appropriate sealing material. The rods are then ground down to the required thickness. In the course of such grinding, all of the wire is ground away except the part which exists between the abutting rods. In order to further reduce the wire capacity, some of the sealing compound is removed from the vicinity of the wires between the abutting rods without impairing the strength of the seal. The portion of the sealing compound which is removed is that on the side of the wire-writing array which faces the cathode-ray beam inside the tube.

The novel features that are considered characteristic of this invention are set forth with particularity in the appended claims. The invention itself, both as to its organization and method of operation, as well as additional objects and advantages thereof, will best be understood from the following description when read in connection with the accompanying drawings, in which:

' Figures 1A through 1B show the successive steps of the method of constructing a short-wire-writing array in accordance with this invention;

Figure 2 is another form of the embodiment of the invention which is preferred; and

Figure 3 shows how the embodiment of the invention is mounted in the face of an electrostatic writing tube.

In describing the method and means of this invention, reference is made to Figures 1A through 1E. As shown in Figure 1A, a rod 10 of an insulating material such as glass, which may have a rectangular shape, has wound thereon at a desired pitch the wire 12, which is to become the writing-wire array. In Figure 1B, a second glass rod 14 is abutted against the first glass rod 10, with the writing wire 12 wound thereon. In addition, a suitable sealing compound 16, which is preferably a glass frit. is placed between the two abutting glass rods for the purpose of holding them and the writing wires in position.

As shown in Figure 1C, the front face of the glass rods is ground away, and in the process of such grinding, the writing wires on the front-face side are removed also. Figure 1D shows the result after all grinding has been completed. The glass rods have been ground until they have the desired thickness. In the course of such grinding, all of the writing wire portions which are not between the abutting edges of the two glass rods have been ground away. Therefore, effectively it can be said that a plurality of wires extend in single file between the abutting glass rods and each of these wires has a length substantially equal to the length of the abutting surfaces.

Figure 1B shows an enlarged cross section of the embodiment of the invention for the purpose of showing the results of the next step after Figure 1D. This next step is to remove a portion of the sealing compound 16, which as indicated is glass frit. A preferred method for removing the glass frit is to use a suitable etchant, such as nitric acid, which will attack the glass frit more rapidly than the glass or wire. The etchant thus may be considered selective in its attack. The sealing compound is removed to expose a portion of the writing wire at one end. This one end is the end which will be in,-

side the writing tube. The glass frit may be removed without impairing the strength of the seal. In this manner, a greater area of the writing wire is exposed to the electron beam, while the interwire capacitance, as well as the capacitance to ground, is still further reduced. The initial reduction of the interwire capacitance and capacitance to ground is achieved by reducing the wires to a minimal required length by grinding away all portions of the wire which are not between the abutting surfaces of the glass blocks. Since the thickness of these blocks may be advantageously made as little as .040 of an inch, it will be appreciated that the interwire capacitance is made extremely small by the method described hereinabove.

Figure 2 shows a preferred shape for the abutting surfaces of the glass blocks whereby a greater area of the wire may be exposed to the electron beam. The advantage of this, of course, is that the wire can charge up to a writing or discharge potential more rapidly with an increased area of exposure. As shown in Figure 2, there are two glass blocks 20, 22, which have their abutting surfaces at an angle to the other surfaces of the glass blocks. The wire 24 has a portion of its length at one end exposed by reason of the removal of some of the sealing compound 26, which holds the wires and glass blocks in position.

Figure 3 shows how the embodiment of the invention comprising the short wire writing array 30 is mounted in the face 32 of an electrostatic writing tube 34.

As a result of the method described above, a writing wire array with a minimal interwire capacitance and capacitance to ground is obtained by making the wires as short as possible and, further, by the removal of the sealing material from a portion of the writing wires. In consequence thereof, a maximum resolution in writing with the electrostatic writing tube is achieved as well as an increase in the speed of writing.

There has accordingly been described and shown herein a novel and useful method and means for producing a novel, short wire writing array for an electrostatic writing tube.

We claim:

1. A writing wire target for an electrostatic writing tube comprising a first and a second glass rod in abutting relationship, a plurality of wires sandwiched in spaced single file between said abutting first and second rods, each of said plurality of wires extending only the length of the abutting surfaces of said first andsecond glass rods, and a sealing compound between the abutting surfaces of said first and second glass rods for holding said first and second glass rods and said writing wires in position, said sealing compound covering all but a portion of said writing wires at one end.

2. A writing wire target for an electrostatic writing tube comprising a first and a second glass rod in abutting relationship, the abutting surfaces of said first and second rods being parallel to one another and making an acute angle with one of the other nonabutting surfaces of said' rods, a plurality of wires sandwiched in spaced single file between said abutting first and second rods, each of said plurality of wires extending only the length of the abutting surfaces of said first and second glass rods, and a sealing compound between the abutting surfaces of said first and second glass rods for holding said glass rods and. writing wires in position, said sealing compound covering all but a portionof said writing wires at onev end.

References Cited in the file of this patent UNITED STATES PATENTS 2,273,793. Ekstrand Feb. 17, 1942 2,283,148 Bruce May 12, 1942 2,657,378 Gray Oct. 27, 1953 2,829,025 Clemens Apr. 1, 1958 

